Calculating Final Angular Velocity of Turntable with Runner on a Horizontal Axis

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Homework Help Overview

The problem involves a runner on a horizontal turntable, requiring the calculation of the final angular velocity of the turntable as the runner slows down to a stop relative to the Earth. The scenario includes parameters such as the runner's mass, velocity, the turntable's initial angular velocity, radius, and moment of inertia.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the conservation of angular momentum and the implications of the runner's change in velocity. There are questions about the clarity of variable definitions and the readability of the working shown. Some participants express confusion about the problem's requirements and seek clarification on their approaches.

Discussion Status

The discussion is ongoing, with participants sharing different interpretations and calculations. Some have provided feedback on the clarity of the original poster's work, while others are attempting to reconcile their answers with the problem's conditions. There is no explicit consensus on the correct approach or final answer yet.

Contextual Notes

Participants note issues with variable definitions and the format of the original post, which may hinder understanding. The problem's specific wording regarding the runner's state relative to the Earth is also under scrutiny.

reminiscent
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Homework Statement


A 55 kg runner runs around the edge of a horizontal turntable mounted on a vertical, frictionless axis through its center. The runner's velocity relative to the Earth has magnitude of 3.1 m/s. The turntable is rotating in the opposite direction with an angular velocity of magnitude 0.20 rad/s relative to the earth. The radius of the turntable is 3.0 m, and its moment of inertia about the axis of rotation is 120 kg-m2. Find the final angular velocity of the turntable if the runner slows to a walk in such a way that she is at rest relative to the earth.

Homework Equations


ΔL = 0
L1 = L2

The Attempt at a Solution


This was ripped off from a problem in the book that asked for "the final angular velocity of the system if the runner comes to rest relative to the turntable," which I did just that, but I just noticed that this problem's last sentence is a different variation (final angular velocity of the turntable if the runner slows to a walk in such a way that she is at rest relative to the earth.")
Here is what I did - should I change anything at the end?
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Your working is not easy to read (posting images is for diagrams and printed/typed matter) and you do not define your variables, which makes it hard to follow.
I get a different answer.
 
haruspex said:
Your working is not easy to read (posting images is for diagrams and printed/typed matter) and you do not define your variables, which makes it hard to follow.
I get a different answer.
Well T stands for turntable and R stands for runner. L1 was the initial and L2 was the final. L1 consisted of the angular momentums of both the turntable and runner. I treated them as a system at the end having the same angular velocity.
 
Can anyone tell me what I did wrong?
 
haruspex said:
Your working is not easy to read (posting images is for diagrams and printed/typed matter) and you do not define your variables, which makes it hard to follow.
I get a different answer.
I got a new answer of -4.06 rad/s.
 
reminiscent said:
I got a new answer of -4.06 rad/s.
That's right.
 

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